Infant malnutrition is the most serious problem that mankind confronts today. Malnutrition has a profound effect both on the physical and psychological growth and development of children. The earlier the malnutrition, the more severe and permanent are the effects. Therefore it would seem that the first priority should be the elimination of malnutrition in the first months of life. It is accepted today that the age at which malnutrition is affecting children is changing: as countries begin to industrialize, breast feeding becomes less frequent and malnutrition occurs at an earlier age. Chile, one of the more rapidly industrializing countries, is suffering now this situation and more developing countries will suffer the same circumstances in the near future. It is necessary to anticipate these changes and the best way is to increase the knowledge of pathogenesis (metabolic and biochemical alteration) of malnutrition. Which are the mechanism of these alterations? Are they definitive? How we can prevent or treat them when they are already produced? The proposed research is part of a wide project dealing on infantile malnutrition on which the authors have been working for more than ten years trying to answer these and many others questions.